Combustion-powered fastener-driving tools, for driving fasteners into workpieces or substrates, are conventionally well-known and are highly desirable within the industry in view of the fact that they provide users with the ability to drive fasteners into the workpieces or substrates independent of any cord or hose attachments to remote power sources. These tools normally comprise a combustion chamber, an on-board fuel supply, means for igniting a combustible gaseous mixture within the combustion chamber, and an expansion volume-driven piston having a driver blade operatively connected thereto for driving fasteners out from the tool and into the workpieces or substrates. It is further known that the effective fastener-driving power for these tools is dependent upon the initial absolute pressure of the combustible gaseous mixture at the time of ignition, the rate at which the gaseous mixture burns within the combustion chamber, the controlled retarded movement of the piston while combustion takes place, and the maximum combustion pressure that can be achieved. In view of the fact that the burn rate is directly proportional to turbulence, a first known type of combustion-powered fastener-driving tool achieves a high burn rate by having a fan disposed within the combustion chamber for the creation of turbulence. The burn rate is therefore rapid enough such that a high combustion pressure level can be desirably achieved within this tool before the piston-driver blade assembly can move to a great degree.
A second known type of combustion-powered fastener-driving tool utilizes a two or dual combustion chamber system comprising, for example, a pre-combustion chamber and a final combustion chamber, and wherein a one-way valve member is interposed between the two combustion chambers so as to control the fluid flow between the two combustion chambers whereby a higher maximum combustion pressure is able to be achieved within the second or final combustion chamber. The first or pre-combustion chamber has an elongated configuration whereby the aspect ratio thereof, which is defined as the ratio of the longitudinal length of the pre-combustion chamber relative to the width or diametrical extent of the pre-combustion chamber, is greater than two. As a result of such structure, the unburned air-fuel mixture is forced ahead of the flame front as it progresses from the upstream ignition end of the pre-combustion chamber toward the downstream end of the pre-combustion chamber within which the one-way valve member is located. Combustion occurs within the second or final combustion chamber when the flame front passes through the one-way valve member into the second or final combustion chamber wherein the final maximum combustion pressure achieved within the second or final combustion chamber is directly proportional to the amount of the combustible mixture pushed into the second or final combustion chamber from the first or pre-combustion chamber. By constructing the pre-combustion chamber with a relatively high aspect ratio, it was discovered that more unburned fuel and air can be pushed ahead of the flame front and into the final combustion chamber than was previously possible with conventional combustion chamber systems characterized by low aspect ratios, whereby the combustion pressure within the final combustion chamber was elevated thereby leading to more efficient combustion within the final combustion chamber and the generation of higher operating pressures to be impressed upon the working piston-driver blade assembly.
An example of such a dual combustion chamber system is disclosed within the United States patent application entitled COMBUSTION-CHAMBER SYSTEM WITH SPOOL-TYPE PRE-COMBUSTION CHAMBER which was filed on Jan. 16, 2002 in the name of Donald L. Van Erden et al. and assigned Ser. No. 10/050836, the principles of which are incorporated herein by reference. A third known type of combustion-powered fastener-driving tool is substantially similar to the second known type of combustion-powered fastener-driving tool except that additional structure is incorporated within the tool for positively restraining any movement of the piston until the air-fuel mixture is ignited within the second or final combustion chamber.
While the aforenoted combustion-powered fastener-driving tools comprise and exhibit various positive structural and operational features and have therefore obviously been commercially successful, such combustion-powered fastener-driving tools also have or exhibit several operational disadvantages or drawbacks. For example, the use of a fan within the combustion chamber in order to create the requisite amount of turbulence to accelerate the burn rate of the air-fuel combustible mixture nevertheless requires a drive motor. While small compact motors of the type required for operation within such fastener-driving tools are commercially available, the motors are expensive because they must be specially designed and fabricated in such a manner as to be capable of withstanding the repetitive jarring forces characteristic of the fastener-driving operations. In addition, the motors also experience periodic failure thereby requiring the tool to be regularly serviced. In a similar manner, while the use of one-way flow check valves at the aforenoted locations between the pre-combustion and final combustion chambers in order to effectively prevent pressure losses due to backflow from the final combustion chamber to the pre-combustion chamber, the check valves must also be specially designed so as to be light enough to permit the unobstructed flow of both the unburned air-fuel mixture and the propagating flame front in the forward direction, and yet be rugged enough to be capable of resisting the high stresses imposed thereon when it moves to its CLOSED position when combustion is initiated within the second or final combustion chamber. In particular, experience has shown that such valves often distort and deform within relatively short periods of time or as a result of a relatively small number of operational cycles thereby requiring their frequent replacement. Lastly, while the piston-restraining systems may exhibit optimal operational characteristics as considered or viewed from a properly timed combustion point of view, such systems obviously require the use of additional components which add cost and weight factors to the tools, as well as additional maintenance requirements.
In order to further attempt to control the generation of turbulence within the combustion chamber, the burn rate of the air-fuel mixture within the combustion chamber, and the propagation flow rate of both the unburned air-fuel mixture and the flame front within the combustion chamber, another type of conventional or PRIOR ART combustion-powered fastener-driving tool is disclosed within U.S. Pat. No. 4,773,581 which issued to Ohtsu et al. on Sep. 27, 1988. Briefly, as can be appreciated from FIG. 1, which corresponds substantially to FIG. 1 of the noted patent, the combustion-powered fastener-driving tool is seen to comprise a cylindrical housing or cylinder head 1 wherein, for example, the upper end of the housing or head 1 is closed while the lower end of the housing or head 1 is open as at 1a. The cylinder head or housing 1 effectively defines a combustion chamber 22, and a second cylinder 2 is fixedly connected in a substantially coaxial manner to the lower end of the cylinder head or housing 1 so as to effectively define a piston chamber within which a piston 3 is movably disposed. A cylindrical guide member 4 is fixedly connected in a substantially coaxial manner to the lower end of the second cylinder 2, and a fastener magazine 7, housing a plurality or strip of fasteners 5, is fixedly attached to a side wall of the cylindrical guide member 4 so as to permit the serial feeding of the plurality of fasteners 5 into an internal guide bore 4a defined within the guide member 4. An upper end portion of a fastener driver or drive rod 6 is fixedly attached to the piston 3, while a lower end portion of the fastener driver or drive rod 6 is coaxially disposed within the guide bore 4a of the guide member 4.
Accordingly, when the piston 3 is forced downwardly under combustion conditions initiated when the tool is fired, the fastener driver or drive rod 6 will drive the leading fastener 5 through the guide bore 4a of the guide member 4 so as to be discharged from the tool. In order to achieve combustion conditions within the tool, a fuel supply device 8 is operatively connected to an upper end portion of the housing or head 1 so as to inject fuel into the upper end portion of the combustion chamber 22, and in a similar manner, an air supply device 9 is likewise operatively connected to an upper end portion of the housing or head 1 so as to inject air into the upper end portion of the combustion chamber 22 whereby the air and fuel injected into the combustion chamber 22 will form an air-fuel mixture. A high tension generator 11, for generating a high voltage discharge, is mounted upon the upper end wall of the housing or head 1 and has a spark plug 12 operatively connected thereto for generating an ignition spark when energized by the generator 11. In order to enhance the turbulence and the mixing together of the air and fuel components of the air-fuel mixture charged into the combustion chamber 22, a plurality of gratings or grilles 14a, 14b, 14c, 14d are disposed within the combustion chamber 22 so as to extend transversely across the combustion chamber 22 and thereby be disposed within parallel planes which are substantially perpendicular to the longitudinal axis of the tool. Accordingly, the grilles 14a, 14b, 14c, 14d effectively divide the combustion chamber 22 into sub-combustion chambers 22a, 22b, 22c, 22d, 22e. In particular, each one of the grilles or gratings 14a-14d may comprise, for example, a perforated disc wherein a plurality of apertures 13 are effectively defined between a network of wall portions 23.
In operation, when air and fuel have been injected into the sub-combustion chamber 22a so as to form an air-fuel mixture, and when such air-fuel mixture has effectively filled the entire combustion chamber 22 as a result of movement or migration from sub-combustion chamber 22a into sub-combustion chambers 22b-22e through means of the apertures 13 respectively defined within the gratings or grilles 14a-14d, the high tension generator 11 is energized so as to in turn cause the spark plug 12 to generate an ignition spark. As is known, when the spark ignites the air-fuel mixture within the sub-combustion chamber 22a, the mixture burns and a flame occurs. The resulting combustion gas within the sub-combustion chamber 22a expands and forces the unburned mixture toward the piston 3 through means of the apertures 13 defined within the gratings or grilles 14a-14d. As the unburned mixture successively passes through the apertures 13 defined within each one of the gratings or grilles 14a-14d, the network of wall portions 23 comprising the gratings or grilles 14a-14d effectively form obstacles to the flow of such unburned mixture, and, in turn, the obstacles effectively cause turbulence within the downstream regions of the unburned mixture. Accordingly, as the flame also traverses the grating or grille 14a through means of the apertures 13, and as a result of the turbulence generated within the unburned air-fuel mixture, it is stated that the flame front advances at a higher rate of speed within the sub-combustion chamber 22b. In turn, the higher rate of speed of the flame front increases the speed of expansion of the resulting combustion gas thereby also increasing the speed of flow of the unburned mixture from the sub-combustion chamber 22b to the sub-combustion chamber 22c. 
As a result, stronger turbulence occurs within the unburned air-fuel mixture present within the sub-combustion chamber 22c, and in turn, the stronger turbulence within the unburned air-fuel mixture present within the sub-combustion chamber 22c causes the flame front to proceed or advance at a rate of speed which is higher or greater than that present within the preceding sub-combustion chamber 22b. Therefore, according to the disclosure of such patent, it is also stated that the speed of the flame front progressively increases each time it successively passes through each one of the grilles or gratings 14a-14d. In this manner, the rapid combustion of the air-fuel mixture is apparently ensured so as to empower the piston 3 and the fastener driver or drive rod 6 whereby a leading one of the fasteners 5 can be driven out from the tool and into the particular workpiece or substrate. It is therefore noted that while the aforenoted PRIOR ART combustion-powered fastener-driving tool of Ohtsu et al. comprises the use of obstacle structures within the sub-combustion chambers in order to advantageously successively or serially affect the turbulence conditions, the burn rate of the air-fuel mixture, and the propagation flow rate of both the unburned air-fuel mixture and the flame front, within the plurality of sub-combustion chambers 22a-22e, it is submitted that the PRIOR ART combustion system of Ohtsu et al. comprises a combustion system which effectively exhibits a cascade type mode of combustion which is not truly advantageous in connection with the promotion or development of the aforenoted attributes or characteristics.
More particularly, in practice, the effectiveness of the provision or presence of the successive orifice plates rapidly deteriorates because each successive plate or screen actually results, even briefly, in a momentary interruption of the propagation speed of the flame front before it again regenerates the turbulence needed to maintain or enhance the propagation speed of the flame front. In addition, the structure of Ohtsu et al. does not provide adequate separation of the unburned and burned components of the air-fuel mixture. Advantageously, each plate structure of Ohtsu et al. causes the flame front to be divided into a plurality of segments or fingers which increases the surface area so as to enhance the burn rate, however, the plates also tend to cause the flame front or burning to proceed or occur laterally as well as forwardly thereby mixing together the burned and unburned components of the air-fuel mixture and causing dilution in the burning properties of the system. Still further, it does not appear that the combustion system of Ohtsu et al. viably achieves various operational parameters which are deemed crucial or critical to desired operational levels of current state-of-the-art technological combustion-powered fastener-driving tools. More particularly, the combustion system of Ohtsu et al. does not appear to be concerned with a dual combustion chamber system, and does not appear to be capable of optimally controlling, both in enhancement and retardation modes, the rate of burn of the air-fuel mixture, as well as the speed at which the flame jet or flame front not only propagates within and through, for example, a pre-combustion chamber of a dual combustion-chamber system, but in addition, the speed at which the flame jet or flame front enters the final combustion chamber. Still yet further, the system of Ohtsu et al. also does not appear to comprise means for ensuring that the entire unburned air-fuel mixture within the final combustion chamber is in fact fully and rapidly ignited such that a peak amount of pressure is effectively impressed upon the working or fastener-driving piston, without any deleterious backward or reverse reflection therefrom, so as to in turn develop the desired amount of peak energy or power for axially moving the working piston-driver blade assembly so as to discharge the fasteners from the tool and to drive the same into a particular workpiece or substrate.
A need therefore exists in the art for a new and improved combustion chamber system for use within a combustion-powered fastener-driving tool, and a new and improved combustion-powered fastener-driving tool having the new and improved combustion chamber system incorporated therein, for optimally controlling, both in enhancement and retardation modes, the rate of burn of the air-fuel mixture, and the speed at which the flame jet or flame front not only propagates within and through, for example, a first pre-combustion chamber of a dual combustion-chamber system, but in addition, the speed at which the flame jet or flame front enters the second or final combustion chamber, and still further, a system for ensuring that the entire unburned air-fuel mixture within the second or final combustion chamber is in fact fully and rapidly ignited such that a peak amount of pressure is effectively impressed upon the working or fastener-driving piston, in the shortest amount of time, without any deleterious backward or reverse reflection therefrom, so as to in turn develop the desired amount of peak energy or power for moving the working piston-driver blade assembly so as to discharge the fasteners from the combustion-powered fastener-driving tool and for driving the fasteners into a particular workpiece or substrate.